1. Field of the Invention
The present invention relates to vortex generators, and more particularly to vortex generators mounted to substantially continuous aerodynamic surfaces to energize boundary layer air to at least partially alleviate the onset of separated flow over the surfaces.
2. Background Art
It has long been known that aerodynamic performance can be improved by generating vortices at selected locations on aerodynamic surfaces. For example, it is a common practice to place vortex generators at certain selected locations on an upper surface of an airfoil to extend the onset of flow separation. By creating the vortex, the high momentum fluid particles outside the boundary layer are mixed with the retarded boundary layer air at the surface, thus avoiding or extending the occurence of separated flow.
A common type of prior art vortex generator is in the form of a small rectangular plate, with the plane of the plate extending vertically upward from the wing surface and slanted moderately relative to the direction of air flow. Another type of prior art vortex generator also has an upright planar configuration, but has its leading edge slanting in an upward and rearward direction to the forward point of the top edge of the vortex generator, and with the top edge extending generally horizontally and rearwardly from the leading edge. Thus, in side elevation, the configuration of the vortex generator comprises a forward triangular portion and a rear rectangular portion, both the triangular and rearward rectangular portions being aligned with one another.
A search of the patent literature has revealed a number of patents. These are the following:
U.S. Pat. No. 2,532,753, Beman, shows a particular configuration of a wing where there is a plurality of fences or ridges positioned in tapered depressions formed in the aft section of the wing.
U.S. Pat. No. 2,800,291, Stephans, shows devices which are alleged to beneficially affect the problems of boundary layer flow in a manner to delay or prevent a separation by maintaining thinness of the boundary layer over a relatively greater distance. These devices are generally triangularly shaped, with the broader base of the triangle having a shallow height dimension and with the height of the tapering triangle increasing in a rearward direction of flow.
U.S. Pat. No. 3,129,908, Harper, shows a plurality of bladder-like devices mounted to the top surface of an airfoil. These bladders can be inflated to change the camber of the airfoil.
U.S. Pat. No. 3,288,399, Gaster, shows a device used on a swept leading edge to prevent spanwise propagation of a turbulent boundary layer. There is a forward relatively blunt portion, and the trailing rearwardly sloping portion blends smoothly into the leading edge.
U.S. Pat. No. 3,438,597, Kasper, shows an aircraft design where there are at the outer tips of the wings vertical stabilizers.
U.S. Pat. No. 3,463,418, Miksch, shows a vortex generating device mounted to an upper forward surface portion of a wing. This device has, in cross-sectional configuration taken parallel to the leading edge, a generally corrugated configuration.
U.S. Pat. No. 3,471,107, Ornberg, shows a device for stabilizing the two leading edge vortices that are formed at each side of the centerline of a thin, sharply swept-back delta wing. The oppositely rotating vortex is generated by a triangle plate projecting upwardly from the suction surface, or by a slot opening to the suction surface from which pressurized air issues.
U.S. Pat. No. 3,578,264, Kuethe, shows a device for amplifying streamwise vortices, making use of the effect known as the "Taylor-Goertler Instability" which results in streamwise vortex generation where a fluid is caused to flow over a concave surface. A second or following properly spaced concave surface results in the amplification of the vortex.
U.S. Pat. No. 3,744,745, Kerker et al, shows a pair of lifting vanes attached to the sides of a nacelle to generate vortices which sweep from the nacelle upwardly over the upper surface of a wing.
U.S. Pat. No. 3,776,363, Kuethe, is intended to reduce the noise and instability due to the shedding of cross-stream vortices caused when air or fluid moves over the trailing edge of a plate, blade, vane or the like. The particular configuration of the vortex generators shown have a generally rounded cross-sectional configuration, in the form of a portion of a semi-circle.
U.S. Pat. No. 3,845,918, White, shows a vortex dissipating device for the tip of an airfoil or a hydrofoil in the form of a fixed plate secured to the tip and aligned with the free stream direction.
U.S. Pat. No. 4,067,518, Patterson et al, shows an aerodynamic body mounted on the wing trailing edge, having its maximum cross-section located approximately at the trailing edge. The greater portion of the body is located below the chord line of the wing. The patent alleges that this creates a strong, negative pressure at the wing trailing edge so as to provide suction of the adjacent upper surface boundary layer air, thus reducing its depth and hence reducing wing drag.
U.S. Pat. No. 4,238,094, McGann, shows a "fluid fence" mounted at the tip portions of an airfoil. The lower edge surface of each fence curves concavely, upwardly away from the wing surface.
U.S. Pat. No. 4,323,209, Thompson, shows a plurality of fingers extending forwardly from the leading edge of the wing. Each finger generates counter rotating vortices that come into contact with one another.
Canadian Patent No. 595,988, Gould et al, shows a vortex generator for an airfoil or the like where the leading edge of the vortex generator slants upwardly and rearwardly from the lower forward end of the leading edge, with the edge extending upwardly and then joining a rearwardly extending edge at a relatively sharp corner. Various other configurations, showing a variety of pointed and/or curved leading edges are illustrated in the latter portion of the drawings of that patent.
Swedish Patent No. 160,134, relates to vortices which are generated over a delta wing surface.